Since the early 1960s there has been a strong connection between surfing and skateboarding that has influenced the history of skateboard design as well as the larger culture of board sports. Terms like “sidewalk surfing” and “surfing-like ride and feel” speak to this connection and have been used to describe ways skateboards attempt to mimic the sensations and ride dynamics of surfing.
Surfing, and other board sports share common ride dynamics of deep deck lean, stability at speed and the ability to “carve” turns.
“Carving” is the ability to make turns and control speed and is associated with deep deck lean and a feeling of “sinking into” the turn such that the deeper the deck or board is leaned the stronger the carving sensations. Carving turns typically involves higher speed and higher turn forces that must be matched by rider input, commitment, and advanced skill. With carving there is also a weightless, floating sensation experienced in the transition between linked turns.
The lean-steering mechanism of skateboards, skates and the like is commonly referred to as the “truck-assembly”, or simply a “truck”. A skateboard truck typically comprises two rigid bodies: a baseplate mounted to a deck and a hanger that supports two laterally spaced wheels that roll on the ground. The rigid bodies of baseplate and hanger are kinematically linked so as to allow rotation relative to each other about a common axis defined by the geometry of the baseplate called here the “hanger pivot axis”.
A skateboard typically comprises a deck upon which the rider stands and a pair of trucks symmetrically mounted to each end of the deck. When constrained by the plane of the ground, a rider standing on the deck leans the deck right to steer right and left to steer left.
Existing skateboard trucks known as fixed king pin trucks consist of mechanisms with two rigid bodies. The present invention introduces a new class of skateboard truck with three rigid bodies, two degrees of freedom, and three primary motions which provide deep deck lean, improved steering control, improved stability at speed, and improved suspension. By delivering this combination of functional attributes the present invention is thus of great use to skateboard riders in search of a more powerful surfing-like ride feel.
Fixed Kingpin Trucks—Kinematic Description (Description of Movement).
Fixed kingpin trucks are a class of trucks that utilize two rigid bodies: (1) a baseplate with a fixed kingpin, PA1; and (2) a hanger with an axle PA2 that supports—a pair of laterally spaced wheels that roll on the ground. With fixed kingpin trucks the baseplate and hanger are connected and constrained by two semi-spherical joints PA11 and PA12 that together allow a single degree of freedom relative to each other, namely rotation about a common axis PA14 called here the “hanger pivot axis”.
The baseplate of a fixed kingpin truck is a first rigid body with a hemispheric recess PA108 called a pivot cup that receives the end of the pivot arm PA201 of the hanger to form a first semi-spherical joint PA11. The baseplate also has a kingpin PA300 that extends downward at an inclined angle. The kingpin is typically fixed to the baseplate by press fit, threaded, or bolted connections, and therefore functions as a single rigid body with the baseplate.
The second rigid body is the hanger PA2 with a pivot arm PA201 that is received within the hemispheric recess PA108 of the baseplate PA1. The hanger also has a centrally positioned, ring shaped yoke PA202 that receives the fixed kingpin PA300 of the baseplate. When assembled the ring shaped yoke of the hanger is sandwiched between elastomeric bushings PA350 and PA351 to form a second semi-spherical elastomerically constrained joint PA12. The elastomeric bushings are integral to truck assembly and provide a return-to-center force.
Hanger axle members support a pair of laterally spaced wheels. Assembly is typically completed by tightening the kingpin nut PA307 to preload the elastomeric bushings PA350 and PA351 and constrain the yoke surfaces of the hanger with the fixed kingpin PA300. Tightening the kingpin nut also constrains the first semi-spherical joint PA11 of the baseplate pivot cup PA108 and hanger pivot arm PA201 from coming apart.
A “hanger pivot plane” PA10 is a central longitudinal plane of the baseplate perpendicular to the mounting surface of the baseplate with the deck and coincident with the axis of the fixed kingpin. With fixed kingpin trucks the hanger pivot plane remains perpendicular to the baseplate and coincident with the centroid point of the first and second semi-spherical joints.
With fixed kingpin trucks the “hanger pivot axis” PA14 is a single axis of rotation between the rigid bodies of baseplate and hanger. The hanger pivot axis is defined by the centroid points of the first and second semi-spherical joints and is coincident with the hanger pivot plane.
A “hanger pivot axis angle” PA19 is defined by the inclined angle of the hanger pivot axis relative to the top surface of the baseplate that supports the skateboard deck.
A “virtual pivot point” PA16 is located at the intersection of the hanger pivot axis PA14 and a line PA21 vertically projected from the center of the hanger axle axis. The assembly of a skateboard with two fixed kingpin trucks creates a single deck roll axis called here the “virtual pivot point roll axis” PA17 that is defined by the virtual pivot points of the front and rear trucks.
Fixed Kingpin—Kinetic Description (Description of Forces that Cause Motion).
In use a rider stands on the deck of an assembled skateboard and the wheels are constrained by the plane of the ground. On a skateboard with fixed kingpin trucks rider input to lean the deck directly causes the rotation of the deck and baseplates and hanger pivot plane to rotate about the virtual pivot point roll axis and the hangers to rotate about the hanger pivot axis of the each truck resulting in the classic lean-steering response of the wheels on the ground. Springs or elastomeric components provide a return to center force.
Fixed Kingpin Trucks—Ride Dynamics.
Fixed kingpin trucks typically have a limited range of adjustment which is not ideal because the firmness of the elastomeric bushing and preload adjustment must match both rider weight and specific style of riding. As well, fixed kingpin trucks with bushings that are too soft for rider weight, are worn, or are too loosely adjusted become unstable at higher speeds. Consequently riders must carefully choose between bushing durometer and preload adjustments that favor deeper deck lean and turning at slower speed or limited deck lean and greater stability at higher speed.
Design and geometry of fixed kingpin trucks have become specialized and optimized for specific speed ranges requiring riders to choose between (1) fixed kingpin trucks optimized for deeper deck lean and tighter turning at slower speed but lack stability at higher speed, or (2) fixed kingpin trucks optimized for stability at higher speed that consequently have a limited range of deck lean and do not turn well at slower speed.
With this specialization, skateboards with fixed kingpin trucks are not able to deliver the combined functionality of deep deck lean, turning, and stability across all speed ranges.